1. Field of the Invention
The present invention relates to microwave power couplers and diplexers and more particularly to transmission line to waveguide diplexers.
2. Description of the Related Art
Communications satellites often employ reflector-type antennas to transmit and receive information-carrying microwave frequency power. Generally, an array of microwave feed horns communicates microwave power between such an antenna reflector and satellite signal processing systems. Information-carrying microwave power to be transmitted by the satellite is provided by transmitter signal processing systems to the feed horn array which directs the transmitted power to the reflector antenna which in turn reflects the transmitted power to a prescribed region on the surface of the earth, and information-carrying microwave power received by the satellite from the earth is reflected by the reflector antenna to the feed horn array which directs the received power to appropriate receiver signal processing systems.
Typically, transmitted and received microwave power occupies different frequency bands in order to maintain adequate signal isolation. For example, the transmitted power might be in a frequency band centered at about 4 GHz, and the received power might be in another frequency band centered at about 6 GHz. Since the same feed horn array conducted power in both frequency bands, means were provided for coupling the respective 4 GHz transmitted power and the 6 GHz received power between the feed horn array and the respective separate transmitter and receiver signal processing systems. Earlier means for coupling power in two such frequency bands are well known. For example, Hudspeth et al, in U.S. Pat. No. 4,533,884 issued on Aug. 6, 1985 discloses a coaxial line to waveguide adaptor suitable for coupling power at approximately 4 GHz and 6 GHz.
More recently, however, there has been a need for communications satellites in which a single reflector antenna and associated feed horn array conducts microwave power in more than two frequency bands which are substantially far apart in the frequency spectrum. For example, in one satellite there is a need for a single reflector antenna and feed horn array which simultaneously can conduct power in a 4 GHz band, a 6 GHz band and a frequency band centered at about 12 GHz. Consequently, there has been a need for coupling means for coupling microwave power in at least two frequency bands which are relatively far apart in the frequency spectrum between a feed horn array and separate ignal processing systems associated with the respective frequency bands.
The provision of such a coupling means, however, presents numerous problems. For example, coupling power in the 12 GHz band to a microwave coupler suitable for conducting power in the 4 GHz and 6 GHz bands could result in distorted antenna horn patterns in the 12 GHz band if unwanted modes were not substantially prevented. Furthermore, unwanted reflections of power in the 4 GHz and 6 GHz bands due to mismatches resulting from components used to couple microwave power in the 12 GHz band should be prevented. Finally, power in the 12 GHz band should be made to propagate between the reflector antenna and the feed horn array and not toward the respective signal processing systems for power in the 4 GHz and 6 GHz bands.
Thus, there has been a need for a coupler suitable for coupling information-carrying microwave power in at least two frequency bands which are substantially far apart in the frequency spectrum between a feed horn array and respective signal processing systems for the respective frequency bands. The present invention meets this need.